Method and device for controlling a storage voltage of a battery pack

ABSTRACT

A storage voltage of a battery pack is controlled with control electronics. The storage voltage of a battery pack is sensed, and a discharge mechanism is triggered if the storage voltage is within a predetermined range of voltage, to thereby adjust the storage voltage of the battery pack to below the predetermined range of voltage, or if the storage voltage is at or above a predetermined voltage, to thereby adjust the storage voltage of the battery pack to below the predetermined voltage. Control electronics sense a storage voltage of a battery pack and trigger a discharge mechanism if the storage voltage is within a predetermined range of voltage, to thereby adjust the storage voltage of the battery pack to below the predetermined range of voltage, or if the storage voltage is at or above a predetermined voltage, to thereby adjust the storage voltage of the battery pack to below the predetermined voltage. The control electronics are coupled to an electronic device and a battery pack. The control electronics are either implemented into the electronic device or the battery pack, or in a separate control electronic device.

RELATED APPLICATION

This application is a continuation of U.S. application Ser. No.11/486,970, filed Jul. 14, 2006 now U.S. Pat. No. 7,656,125, whichclaims the benefit of U.S. Provisional Application No. 60/699,088, filedon Jul. 14, 2005, the entire teachings of which are incorporated hereinby reference.

BACKGROUND OF THE INVENTION

Li-ion batteries in portable electronic devices typically undergodifferent charging, discharging and storage routines based on theirusers. Although it would be advantageous to have relatively longcalendar(or storage) life and/or cycle life of the batteries, typicallythe batteries have limited calendar and cycle lives partly due tochemical degradation of the battery and mechanical degradation caused bythe breathing nature of electrodes, changing their thickness uponlithium intercalation and removal. For example, although Li-ionbatteries employing a manganate-spinel-based cathode material generallyhave higher safety, higher power capability and lower manufacturingcost, compared to those employing a LiCoO₂-based cathode material, theyhave relatively lower cycle and calendar lives. Also, among the sametype of batteries, their calendar and cycle lives can be different fromeach other depending upon charging, discharging and storage routinesthat they undergo based on their users.

Two properties generally are to be considered for the calendar life of abattery. The first property relates to lost capacity of a battery duringstorage via self discharging. It is well known in the battery industrythat a battery that is stored without ability to charge may partiallylose its charge. The level of charge loss generally depends on factorssuch as chemical stability, temperature and storage time. Li-ionbatteries are examples of such batteries that generally lose theircapacity during storage via self discharging. The lost capacity of aLi-ion battery may be measured as the relative state-of-charge change(or voltage change) that a battery undergoes during storage. The secondproperty relates to recoverable capacity and permanent degradation of abattery that is non-recoverable. The recoverable capacity can bemeasured by relating initial capacity during a full charge/dischargecycle to that of a full charge/discharge cycle of a battery that hasbeen stored. The lost capacity of a battery is believed to be related tochemical degradation of the battery during storage, which is differentfrom the degradation caused by cycling a battery. The degradation causedby cycling a battery is believed to include degradation caused by thebreathing nature of electrodes. Regardless, degradation of batteriesconsequent to prolonged periods of use is a pervasive problem for manyelectronic devices, particularly those that employ lithium-ionbatteries.

Therefore, there is a need for developing methods for increasing thecalendar life and/or cycle life of batteries, such as Li-ion batteries.

SUMMARY OF THE INVENTION

The invention generally relates to methods and electronic devices thatcontrol a storage voltage of a battery or battery pack to adjust itsstorage voltage to avoid a detrimental voltage range or a detrimentalvoltage, thereby minimizing the time the battery or battery pack spendsat the detrimental voltage range or the detrimental voltage.

Applicants have now discovered that for Li-ion batteries, and inparticular for Li-ion batteries containing a mixture of a lithiumcobaltate and a manganate spinel, the storage voltage level of a givenbattery (or cell) is a determining factor for the calendar life of thebattery. Applicants have now also discovered that there is a particularstorage voltage range where Li-ion batteries degrade faster. Based uponthese discoveries, a method of controlling a storage voltage of abattery pack with control electronics; a system comprising an electronicdevice, a battery pack and control electronics coupled to the electronicdevice and the battery pack; a battery pack comprising a pack housing,at least one cell in the pack housing and control electronics in thepack housing; and a control electronic device comprising controlelectronics are disclosed herein.

In one embodiment, the present invention is directed to a method ofcontrolling a storage voltage of a battery pack with controlelectronics. The method includes the steps of sensing a storage voltageof the battery pack, sensing a change in the storage voltage over time,and triggering a discharge mechanism if the storage voltage is within apredetermined range of voltage, to thereby adjust the storage voltage ofthe battery pack to below the predetermined range of voltage, or if thestorage voltage is at or above a predetermined voltage, to therebyadjust the storage voltage of the battery pack to below thepredetermined voltage. Preferably, the control electronics and thebattery pack are coupled to an electronic device.

In another embodiment, the present invention is directed to a systemcomprising an electronic device, a battery pack and control electronicscoupled to the electronic device and the battery pack. The controlelectronics sense a storage voltage of the battery pack and trigger adischarge mechanism if the storage voltage is within a predeterminedrange of voltage, to thereby adjust the storage voltage of the batterypack to below the predetermined range of voltage, or if the storagevoltage is at or above a predetermined voltage, to thereby adjust thestorage voltage of the battery pack to below the predetermined voltage.

In yet another embodiment, the present invention is directed to abattery pack comprising a pack housing, at least one cell in the packhousing and control electronics in the pack housing to sense a storagevoltage of the battery pack and to trigger a discharge mechanism if thestorage voltage is within a predetermined range of voltage, to therebyadjust the storage voltage of the battery pack to below thepredetermined range of voltage, or if the storage voltage is at or abovea predetermined voltage, to thereby adjust the storage voltage of thebattery pack to below the predetermined voltage.

The present invention also includes a control electronic device thatincludes a device housing and control electronics in the device housingto sense a storage voltage of a battery pack and to trigger a dischargemechanism if the storage voltage is within a predetermined range ofvoltage, to thereby adjust the storage voltage of the battery pack tobelow the predetermined range of voltage, or if the storage voltage isat or above a predetermined voltage, to thereby adjust the storagevoltage of the battery pack to below the predetermined voltage.

The present invention can enhance calendar life and/or cycle life inbatteries effectively. Typically, Li-ion batteries in portableelectronic devices undergo different charging, discharging and storageroutines based on their users. For example, some users use their deviceson a daily basis starting with a fully charged battery in the morningand at the end of the day they plug their device into the charger inorder to again fully charge the battery. Other users may keep theirfully-charged device plugged to an external power, in which the batteryis at a full state-of-charge, and then may occasionally unplug thedevice, draining the battery. Power drain can also vary greatly betweenusers. In addition, a battery may undergo storage at any givenstate-of-charge for periods of a few hours to several days, or in somecases even weeks or months. With the present invention, a voltage ofsuch batteries while they are not actively being used, i.e., a storagevoltage of the batteries, can be controlled to avoid a predeterminedrange of voltage which can be detrimental for calendar life of thebatteries and thereby enhance the calendar life of the batteries. Thepresent invention is particularly useful for HEV applications that has arequirement of long calendar life, as well as for long lived portabledevices.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic representation of an embodiment of the presentinvention, showing a system of the invention that includes an electronicdevice, a battery pack and control electronics coupled to the electronicdevice, where the control electronics are implemented in the batterypack.

FIG. 2 is a schematic representation of a battery pack of the inventionincluding control electronics that control a storage voltage of thebattery pack.

FIG. 3 is a schematic representation of an embodiment of the presentinvention, showing a system of the invention that includes an electronicdevice, a battery pack and control electronics coupled to the electronicdevice, where the control electronics are implemented in the electronicdevice.

FIG. 4 is a schematic representation of an embodiment of the presentinvention, showing a system of the invention that includes an electronicdevice, a battery pack and control electronics coupled to the electronicdevice, where a component of the control electronics is included in thebattery pack and a component of the control electronics is implementedin the electronic device.

FIG. 5 is a schematic representation of another embodiment of thepresent invention, showing a system of the invention that includes anelectronic device, a battery pack and control electronics coupled to theelectronic device, where a component of the control electronics isincluded in the battery pack and a component of the control electronicsis implemented in the electronic device.

FIG. 6 is a schematic representation of an embodiment of the presentinvention, showing a system of the invention that includes an electronicdevice, a battery pack and control electronics coupled to the electronicdevice, where the control electronics are implemented in a controlelectronic device separate from the battery pack and from the electronicdevice.

FIGS. 7A and 7B are schematic representations of one embodiment ofmethod steps for the control electronics of the invention.

FIGS. 7C and 7D are schematic representations of another embodiment ofmethod steps for the control electronics of the invention.

FIG. 8A is a schematic representation of an example of battery chargingchipset supporting cell balancing from Texas Instruments, which can beused for an electronic circuit for controlling a storage voltage of abattery pack in the invention.

FIG. 8B is a schematic representation of the relationship between FIGS.8B-1 through 8B-7, which, in turn, constitute a schematic representationof another example of a battery charging chipset supporting cellbalancing from Texas Instruments, which can be used for an electroniccircuit for controlling a storage voltage of a battery pack in theinvention (external discharge resistors are circled).

FIG. 8C is a block diagram of a cell balancing circuit with firmwarethat can be used for an electronic circuit for controlling a storagevoltage of a battery pack in the invention.

DETAILED DESCRIPTION OF THE INVENTION

The foregoing will be apparent from the following more particulardescription of example embodiments of the invention, as illustrated inthe accompanying drawings in which like reference characters refer tothe same parts throughout the different views. The drawings are notnecessarily to scale, emphasis instead being placed upon illustratingembodiments of the present invention.

As used herein, the term “storage voltage” means an essentially constantvoltage of a battery pack or battery where the change of the voltageover time is equal to or less than about 0.05 V per day. Thus, anyvoltage change of the storage voltage over time is caused by selfdischarging, but not by drainage due to running an electronic device.For example, the battery pack or battery is at a storage voltage whenthe battery pack or battery is not being used actively for a substantialtime period, such as at least about 30 minutes, at least about 1 hour,or at least about 2 hours. Such cases can be found where the electronicdevice coupled to the battery pack or battery is turned off, or wherethe electronic device coupled to the battery pack is not interactingwith a user for a substantial time period (e.g., at least about 30minutes, at least about 1 hour, or at least about 2 hours), or where anexternal power supply is being used for the electronic device, resultingin a voltage of the battery pack or battery being kept at asubstantially constant voltage, for example at a full state-of-charge(e.g., 4.2 V) for a substantial time period (e.g., at least about 30minutes, at least about 1 hour, or at least about 2 hours).

As used herein, the term “battery pack or battery at a fullstate-of-charge” means a battery pack or battery is at its maximumvoltage, e.g., 4.2 V per block of series cells, a block being one ormore cells in parallel.

FIG. 1 shows system 10 of the invention, which includes electronicdevice 12, battery pack (or battery) 14 and control electronics 16coupled to electronic device 12 and battery pack 14. In this embodiment,control electronics 16 is implemented or incorporated into battery pack14.

Control electronics 16 typically sense a storage voltage of battery pack14 and trigger a discharge mechanism if the storage voltage is within apredetermined range(s) of voltage (e.g., between about 3.85 V and about3.95 V and/or between about 4.15 V and about 4.20 V) to thereby adjustthe storage voltage to below the predetermined range of voltage, or ifthe storage voltage is at or above a predetermined voltage, such as afull state-of charge (e.g., 4.2 V), to thereby adjust the storagevoltage to below the predetermined voltage. Preferably, this triggereddischarge mechanism occurs when a predetermined amount of time haspassed.

In the invention, more than one predetermined range and/or more than onepredetermined voltage can be employed. In one embodiment, there is morethan one predetermined range of voltage that each triggers thedischarging mechanism. In another embodiment, there is more than onepredetermined range of voltage that each triggers the dischargingmechanism, and there is one or more predetermined voltages that eachtrigger the discharging mechanism.

The discharging can be done by any suitable methods known in the art,for example, through a resistive load until the storage voltage becomeslower than the predetermined range of voltage or the predeterminedvoltage. The termination of the discharging can be done by sensing avoltage of battery pack 14 during the discharging, and the dischargingterminates when the voltage reaches a voltage value that is below thepredetermined range of voltage or the predetermined voltage. Preferably,the voltage value at which the discharging terminates is not lower thanabout 3.0 V per cell. More preferably, the voltage value for eachindividual cell or parallel block of cells at which the dischargingterminates is in a range of between about 3.75 V and about 3.85 V, suchas about 3.8 V, or between about 3.95 V and about 4.15 V, such as about4.1 V. Generally, a suitable rate of the discharging is in a range ofbetween about 10 mA and about 50 mA.

As shown in FIG. 1, in a preferred embodiment, control electronics 16includes detector circuit 18 to sense a voltage of battery pack 14 and avoltage change over time, and controller circuit 20 to control a voltageof battery pack 14.

Detector circuit 18 preferably includes a voltage sensor and a timesensor, or a combined voltage- and time-sensor. With such sensor(s),control electronics 16 can sense periodically time (t_(i)) and a voltage(V_(i,j)) of cell(s) j of battery pack 14 at time t_(i). Control circuit20 preferably includes a voltage sensor and a current sensor, or acombined voltage- and current-sensor. With such sensor(s), controlcircuit 20 can discharge battery pack 14 to thereby adjust a voltage(V_(i,j)) of cell(s) j of battery pack 14 below the predetermined rangeof voltage or the predetermined voltage.

The electronic device can be on or off when the discharge mechanism istriggered. Further, the electronic device can be actively used,utilizing an external power source, at the time that the dischargingmechanism is triggered. Alternatively, the electronic device can be on,or activated, but idle (i.e., not being actively used at the time thedischarge mechanism triggered). Similarly, the discharge mechanism canbe triggered while the electronic device is shut off, regardless ofwhether the device is connected to an external power source.

In a specific embodiment, detector circuit 18 senses a time period forwhich electronic device 12 is not interacting with a user, anddetermines if the time period is longer than a predetermined value, andif the storage voltage is within a predetermined range of voltage, or ator above a predetermined voltage at any time during that time period,detector circuit 18 triggers control circuit 20 to initiate thedischarge mechanism. Preferably, the predetermined time value is about30 minutes, preferably 1 hour, more preferably about 2 hours.

In another specific embodiment, detector circuit 18 senses if batterypack 14 is in a charge mode, and senses a time period for the charging.In a more specific embodiment, detector circuit 18 also senses if thevoltage of battery pack 14 is at or above a predetermined value. If thetime period of charging is longer than a predetermined value, and if thevoltage of battery pack 14 is at or above the predetermined value,detector circuit 18 triggers control circuit 20 to initiate thedischarge mechanism to thereby adjust the voltage to below thepredetermined voltage. The discharging mechanism can be operated byturning off charging and initiating discharging. Preferably, thepredetermined time value is about 30 minutes, preferably 1 hour, morepreferably about 2 hours.

In yet another specific embodiment, detector circuit 18 determines ifthe storage voltage of battery pack 14 is kept at a full state-of-chargefor longer than a predetermined time value, such as for longer thanabout 30 minutes, preferably for longer than 1 hour, more preferably forlonger than about 2 hours. This indicates that electronic device 12 isbeing operated by an external power source, rendering battery pack 14not being used and keeping battery pack 14 at its full state-of-charge.Since keeping a battery at its full state-of-charge for a long periodmay reduce the cycle life and safety of the battery, it is advantageousto avoid such a situation. If it is determined that the storage voltageof battery pack 14 is kept at a full state-of-charge for longer than apredetermined time value, detector circuit 18 triggers control circuit20 to initiate the discharge mechanism. Preferably, the predeterminedtime value is about 30 minutes, preferably about 1 hour, more preferablyabout 2 hours.

Referring back to FIG. 1, in the embodiment of FIG. 1, controlelectronics 16 is implemented or incorporated into battery pack 14. Aspecific example of such a battery pack of the invention is shown inFIG. 2. As shown in FIG. 2, battery pack 14 includes pack housing 22 andone or more cells 24 in pack housing 22. One or more control electronics16 are in communication with cells 24. Battery pack 14 can additionallyinclude charger 26 to charge/recharge cells 24. Preferably, the charger26 is coupled with control electronics 16.

Alternatively, control electronics 16 can be implemented or incorporatedinto electronic device 12, as shown in FIG. 3. FIGS. 4 and 5 show otherembodiments where a component of control electronics 16 is implementedor incorporated into battery pack 14 and a component of controlelectronics 16 is implemented or incorporated into electronic device 12.Specifically, FIG. 4 shows system 40 of the invention where detectorcircuit 18 is implemented or incorporated into battery pack 14, andcontroller circuit 20 is implemented or incorporated into electronicdevice 12. FIG. 5 shows system 50 of the invention where detectorcircuit 18 is implemented or incorporated into electronic device 12, andcontroller circuit 20 is implemented or incorporated into battery pack14.

In yet other embodiments, as shown in FIG. 6, control electronics 16 areimplemented or incorporated into separate control electronic device 70that includes device housing 72 and control electronics 16 in devicehousing 72.

When control electronics 16 are implemented or incorporated into eitherelectronic device 12 or battery pack 14, control electronics 16 canoptionally be executed in a microprocessor located inside electronicdevice 12 or battery pack 14. As shown in FIG. 6, when controlelectronics 16 are implemented or incorporated into separate controlelectronic device 70, control electronics 16 can communicate withelectronic device 12, such as a laptop computer, and with battery pack14, through serial communication ports 74 known in the art, for example,serial communication ports SMBC/SMBD.

FIGS. 7A and 7B show flow charts of one embodiment of the invention forcontrolling a storage voltage of battery pack 14 with controlelectronics 16 that are coupled to battery pack 14 and electronic device12. FIGS. 7C and 7D show flow charts of another embodiment of theinvention for controlling a storage voltage of battery pack 14 withcontrol electronics 16 that are coupled to battery pack 14 andelectronic device 12.

As shown in FIGS. 7A and 7C, in step 102 or step 202, controlelectronics 16 read time t_(i), voltage V_(i,j) of individual cells, orof block of cells of battery pack 14 (cell(s) j at time t_(i), andoptionally a status of charging mode (referred to “charge flag” in FIGS.7A and 7C) of battery pack 14. For example, the charge flag is on whenbattery pack 14 is in charge mode, and the charge flag is off when thebattery pack is being used as a power source for electronic device 12.

If the charge flag is not on, control electronics 16, e.g., detectorcircuit 18 of control electronics 16, read V_(i,j) of any cell or ofblock of cells of battery pack 14 (cell(s) j). In one embodiment, asshown in step 106 of FIG. 7A, control electronics 16 determine i) ifV_(i,j) is within a predetermined range, i.e., between about 3.85 V andabout 3.95 V, and also determine ii) if total time t_(tot) (i.e., t2−t1)for which V_(i,j) is within the predetermined range is greater than apredetermined time value t_(set), which can be set, for example, betweenabout 1 and 2 hours. Alternatively, as shown in step 206 of FIG. 7C,control electronics 16 determine i) if V_(i,j) is within a predeterminedrange, i.e., between about 3.85 V and about 3.95 V, and also determineii) if any voltage change over time (*(V_(i=t2)−V_(i=t1))_(j)*/t2−t1) isless than or equal to about 0.05 V/day, preferably less than or equal toabout 0.03 V/day, more preferably less than or equal to about 0.01V/day. If both conditions i) and ii) of step 106 or step 206 are met,detector circuit 18 of control electronics 16 triggers control circuit20 of control electronics to initiate discharging the cell(s) j untilV_(i,j) becomes, for example, 3.85 V (step 108 of FIG. 7A, step 208 ofFIG. 7C).

In yet another alternative embodiment of step 206 (not shown), when thevoltage change over time (*(V_(i=t2)−V_(i=t1))_(j)*/t2−t1) is determinedless than or equal to about 0.05 V/day, preferably less than or equal toabout 0.03 V/day, more preferably less than or equal to about 0.01V/day, discharging may be triggered only if total time t_(tot) (i.e.,t2−t1) for which V_(i,j) is within the predetermined range is alsogreater than a predetermined time value t_(set).

In step 106, if V_(i) is not within a predetermined range, i.e., betweenabout 3.85 V and about 3.95 V, or even if V_(i) is within thepredetermined range, but the total time t_(tot) for which V_(i) iswithin the predetermined range is not greater than a predetermined timevalue t_(set), control electronics 16 moves on step 110. Similarly, instep 206, even if V_(i,j) is within the predetermined range, but if anyvoltage change over time (*(V_(i=t2)−V_(i=t1))_(j)*/t2−t1) is not lessthan or equal to about 0.05 V/day, such as not less than or equal toabout 0.03 V/day, or not less than or equal to about 0.01 V/day, controlelectronics 16 moves on step 110.

As shown in step 110 of FIG. 7A, control electronics 16, e.g., detectorcircuit 18 of control electronics 16, determines i) if V_(i,j) is withina second predetermined range, i.e., between about 4.15 V and about 4.20V, and also determines ii) if total time t_(tot) for which V_(i,j) iswithin the predetermined range is greater than a predetermined timevalue t_(set). Alternatively, as shown in step 210 of FIG. 7C, controlelectronics 16, e.g., detector circuit 18 of control electronics 16,determine i) if V_(i,j) is within a second predetermined range, i.e.,between about 4.15 V and about 4.20 V, and also determine ii) if anyvoltage change over time (*(V_(i=t2)−V_(i=t1))_(j)*/t2−t1) is less thanor equal to about 0.05 V/day, preferably less than or equal to about0.03 V/day, more preferably less than or equal to about 0.01 V/day. Instep 110 or 210, when these i) and ii) conditions are met, detectorcircuit 18 of control electronics 16 triggers control circuit 20 ofcontrol electronics to initiate discharging the cell(s) j until V_(i,j)is below 4.15 V, for example, 4.10 V (steps 110 and 112 of FIG. 7A,steps 210 and 212 of FIG. 7C).

In yet another alternative embodiment of step 210 (not shown), when thevoltage change over time (*(V_(i=t2)−V_(i=t1))_(j)*/t2−t1) is determinedless than or equal to about 0.05 V/day, preferably less than or equal toabout 0.03 V/day, more preferably less than or equal to about 0.01V/day, discharging may be triggered only if total time t_(tot) (i.e.,t2−t1) for which V_(i,j) is within the predetermined range is alsogreater than a predetermined time value t_(set).

When the conditions i) and ii) of step 110 are not met, controlelectronics 16 moves on step 102. Similarly, when the conditions and ii)of step 210 are not met, control electronics 16 moves on step 202.

In each of step 104 of FIG. 7A and step 204 of FIG. 7C, if the chargeflag is on, control electronics follows scenario B shown in FIG. 7B orFIG. 7D. Under scenario B, detector circuit 18 of control electronics 16reads time t_(i) and voltage V_(i,j) of individual cells, or of block ofcells of battery pack 14 (cell(s) j) that is under charging mode, anddetermine whether or not total charging time t^(c) _(tot) is greaterthan a predetermined charging time value t^(c) _(set) (step 116 of FIG.7B, step 216 of FIG. 7D). If total charging time t^(c) _(tot) is greaterthan a predetermined charging time value t^(c) _(set), detector circuit18 of control electronics 16 triggers control circuit 20 of controlelectronics 16 to initiate discharging the cell(s) j until V_(i,j)becomes 4.10 V (step 118 of FIG. 7B, step 218 of FIG. 7D). In thealternative, detector circuit 18 of control electronics 16 triggers acharger (e.g., charger 26 in FIG. 2) that is coupled to controlelectronics 16 to charge the cell(s) j until V_(i,j) becomes 4.10 V. Iftotal charging time t^(c) _(tot) is not greater than a predeterminedcharging time value t^(c) _(set), charging the cell(s) j continued untilV_(i,j) becomes a maximum voltage, for example, 4.20 V (step 120 of FIG.7B, step 220 of FIG. 7D). Once V_(i,j) either fully charged (step 120 ofFIG. 7B, step 220 of FIG. 7D) or charged to V_(i)=4.10 V (step 118 ofFIG. 7B, step 218 of FIG. 7D), control electronics 16 resume scenario Ashown in FIG. 7A or FIG. 7C.

Charging the cell(s) j can be done by any suitable method known in theart, for example, by charger 26 as shown in FIG. 2. Typical chargingcurrents for batteries are in a range of between about 0.7 C and about 1C. Such a charging current is allowed until a maximum voltage (V_(max))is reached, e.g., 4.2 V. Once V_(max) has been reached, the chargingcurrent is lowered by control charging circuitry to disallow any of thecells of battery pack 14 to reach a voltage level higher than 4.2 V.Electronic circuits managing this type of functionality are known in theart, for example, in a U.S. Utility application Ser. No. 11,823,479entitled, “Special Function Battery Pack B,” filed on Jun. 27, 2007 andpublished on Feb. 28, 2008, the entire teachings of which areincorporated herein by reference. Optionally, a fast charge processemploying a relatively high charging current, as described in the U.S.Utility Application entitled “Special Function Battery Pack B” can beimplemented into charger 26 of battery pack.

The predetermined time values t_(set) in steps 106 and 110 and t^(c)_(set) in step 116 can be each independently different or the same.Examples of t_(set) and t^(c) _(set) include any time values in a rangeof between about 30 minutes and about 2 hours, such as between about 40minutes and about 2 hours or between about 1 hour and about 2 hours.

Any suitable electronic circuits known in the art can be used in theinvention, and appropriately programmed with parameters suitable for thedesired applications of control electronics 16 of the invention, forexample as implemented in systems 10, 30, 40, 50 and 60 of theinvention. Each battery manufactured generally has an unique chemistryand interpretation of how the battery can be used in best mode toprovide long cycle life, long storage life, high capacity and highsafety.

One of the parameters that can be controlled by the circuitry is thepredetermined range(s) of voltage. Other parameters that can becontrolled by the circuitry include voltage change over time due to selfdischarging; predetermined time value for charging; predetermined timevalue for which the storage voltage of battery pack 14 is kept at a fullstate-of-charge; voltage of the full state-of-charge; predetermined timevalue for which electronic device 12 is not interacting with a user;discharging rate; and voltage level(s) for termination of thedischarging. These parameters generally depend upon specific types ofcell(s) of battery pack 14.

Examples of electronic circuits diagrams suitable for use in conjunctionwith the invention are shown in FIGS. 8A-8C. FIG. 8A shows an example ofa suitable battery charging/discharging controlling chipset from Texasinstruments (bq29312), with interacting charging/discharging FETs thatare controlled by a microprocessor (available from ti.com). In the Texasinstruments' chipset, the bq29312 (circled in FIG. 8A) is a 2-, 3- or4-cell lithium-ion battery pack protection analog front end (AFE) ICthat incorporates a 3.3.-V, 25-mA low-dropout regulator (DO). Thebq29312 also integrates an I2C compatible interface to extract batteryparameters (e.g., cell voltages and control output status). Currentprotection thresholds and delays can also be programmed into thebq29312. The circuitry has compatible users interface that also allowsaccess to battery information. Chosen predetermined levels of thevoltage and time parameters from the invention would be programmed intothe microprocessor that in turn would control turning the FETs off andon depending on the voltage and time response of each individual cell orcell block.

FIG. 8B shows a reference design of a chipset supporting cell balancingfrom Texas instruments (available from ti.com). The discharge resistorsare circled in FIG. 8B. Under the invention, the microprocessor would beprogrammed to discharge cells that are within the predetermined voltageand time levels through the highlighted external discharge resistors.

FIG. 8C shows a simplified functional block diagram of a chipset knownin the art. The firmware control program would read and control time andvoltage levels according to the invention. Cells are eligible would bedischarged through load resistors.

In the designs of FIGS. 8A-8C, the FETs are inside the chip. In order toenable higher currents for discharge, FETs can optionally be movedoutside the chipset. This provides easier means to manage heat as highcurrent cause heating.

In one embodiment, battery pack 14 includes at least one lithium-ioncell. In this embodiment, preferably, the predetermined range(s) ofvoltage for triggering a discharge mechanism is between about 3.85 V andabout 3.95 V, or between about 4.15 V and about 4.20 V, and thepredetermined voltage is about 4.20 V. In a specific embodiment, twopredetermined ranges of voltage are employed for each triggering thedischarge mechanism, i.e., ranges of between about 3.85 V and about 3.95V, and between about 4.15 V and about 4.20 V. In a more specificembodiment, in addition to the two predetermined ranges, thepredetermined voltage is also employed for each triggering the dischargemechanism.

In a preferred embodiment, battery pack 14 includes at least onelithium-ion cell having the full state-of-charge of 4.2 V.

Cells or batteries for battery pack 14 can be cylindrical or prismatic(stacked or wound), preferably prismatic, and more preferably of aprismatic shape that is oblong. Although the present invention can useall types of prismatic cells or batteries, oblong shape is preferred.

Referring back to FIG. 2, in some embodiments of the invention, batterypack 14 include a plurality of lithium-ion batteries (or cells) (e.g., 2to 5 cells) which are connected with each other in series.Alternatively, battery pack 14 can include a plurality of lithium-ionbatteries (or cells) which are connected with each other in parallel orin series and parallel.

The present invention also includes a battery pack including controlelectronics 16, such as battery pack 14 as described above. A controlelectronic device that includes a device housing and control electronics16, as described above, for example, control electronic device 70, isalso encompassed by the invention. Suitable positive active materialsfor the positive electrodes of the lithium-ion batteries (or cells)include any material known in the art, for example, lithium nickelate(e.g., LiNiM′O₂), lithium cobaltate (e.g., LiCoO₂), olivine-typecompounds (e.g., LiFePO₄), manganate spinel (e.g., Li_(1+x)Mn_(2−x)O₄ orLi_(1+x1)(Mn_(1−y1)A′_(y2))_(2−x2)O_(z1)) and combinations thereof.Various examples of suitable positive active materials can be found ininternational application No. PCT/US2005/047383, and a U.S. patentapplication entitled “Lithium-ion Secondary Battery,” filed on Jun. 23,2006 under the application Ser. No. 11/474,056, the entire teachings ofwhich are incorporated herein by reference.

In one embodiment, each lithium-ion cell included in battery pack 14includes an active cathode mixture that includes a manganate spinel. Ina preferred embodiment, the manganate spinel is represented by anempirical formula ofLi_((1+x1))(Mn_(1−y1)A′_(y2))_(2−x2)O_(z1) where:

x1 and x2 are each independently equal to or greater than 0.01 and equalto or less than 0.3;

y1 and y2 are each independently equal to or greater than 0.0 and equalto or less than 0.3;

z1 is equal to or greater than 3.9 and equal to or less than 4.1; and

A′ is at least one member of the group consisting of magnesium,aluminum, cobalt, nickel and chromium.

In one specifically preferred embodiment, the manganate spinel isrepresented by an empirical formula ofLi_((1+x1))(Mn_(1−y1)A′_(y2))_(2−x2)O_(z1) where A′ includes a M³⁺ ion,such as Al³⁺, Co³⁺, Ni³⁺ and Cr³⁺, more preferably Al³⁺. In anotherspecific embodiment, the manganate spinel is represented by an empiricalformula of Li_((1+x1))(Mn_(1−y1)A′_(y2))_(2−x2)O_(z1) where y2 is zero.More preferably, the manganate spinel for the invention includes acompound represented by an empirical formula of Li_((1+x1))Mn₂O_(z1),where x1 and z1 are each independently the same as described above.Alternatively, the manganate spinel for the invention includes acompound represented by an empirical formula ofLi_((1+x1))Mn_(2−x2)O_(z1), where x1, x2 and z1 are each independentlythe same as described above.

Specific examples of the manganate spinel that can be used in theinvention include LiMn_(1.9)Al_(0.1)O₄, Li_(1+x1)Mn₂O₄,Li_(1+x1)Mn_(2−x2)O₄, and their variations with Al and Mg modifiers.Various other examples of manganate spinel compounds of the typeLi_((1+x1))(Mn_(1−y1)A′_(y2))_(2−x2)O_(z1) can be found in U.S. Pat.Nos. 4,366,215; 5,196,270; and 5,316,877 (the entire teachings of whichare incorporated herein by reference).

In another embodiment, each lithium-ion cell included in battery pack 14includes an active cathode mixture that includes a manganate spinel anda lithium cobaltate. Suitable examples of the manganate spinel are asdescribed above.

Suitable examples of lithium cobaltates that can be used in theinvention include LiCoO₂ that is modified by at least one of modifiersof Li and Co atoms. Examples of the Li modifiers include barium (Ba),magnesium (Mg) and calcium (Ca). Examples of the Co modifiers includethe modifiers for Li and aluminum (Al), manganese (Mn) and boron (B).Other examples include nickel (Ni) and titanium (Ti). Particularly,lithium cobaltates represented by an empirical formula ofLi_(x6)M′_((1−y6))Co_((1−z6))M″_(z6)O₂, where x6 is greater than 0.05and less than 1.2; y6 is equal to or greater than 0 and less than 0.1,z6 is equal to or greater than 0 and less than 0.5; M′ is at least onemember of magnesium (Mg) and sodium (Na) and M″ is at least one memberof the group consisting of manganese (Mn), aluminum (Al), boron (B),titanium (Ti), magnesium (Mg), calcium (Ca) and strontium (Sr), can beused in the invention. Another example of lithium cobaltates that can beused in the invention includes LiCoO₂.

In a specific embodiment, the lithium cobaltate and the manganate spinelfor the invention are in a weight ratio of lithium cobaltate: manganatespinel between about 0.95:0.05 to about 0.55:0.45, preferably betweenabout 0.9:0.1 to about 0.6:0.4, more preferably between about 0.8:0.2 toabout 0.6:0.4, even more preferably between about 0.75:0.25 to about0.65:0.45, such as about 0.7:0.3.

In a more specific embodiment, the lithium cobaltate is LiCoO₂ dopedwith Mg and/or coated with a refractive oxide or phosphate, such as ZrO₂or Al₂(PO₄)₃. In another more specific embodiment, the lithium cobaltateis LiCoO₂ with no modifiers.

In a even more specific embodiment, each lithium-ion cell included inbattery pack 14 includes an active cathode mixture that includesLi_((1+x1))Mn₂O_(z1), preferably Li_(1+x1)Mn₂O₄, and LiCoO₂. In anothereven more specific embodiment, each lithium-ion cell included in batterypack 14 includes an active cathode mixture that includesLi_(1+x1)Mn_(2−x2)O_(z1), preferably, Li_(1+x1)Mn_(2−x2)O₄, and LiCoO₂.

Suitable examples of electronic device 12 for the invention include, butnot limited to, portable power devices, such as portable computers,power tools, toys, portable phones, camcorders, PDAs and HEVs (HybridElectric Vehicles). Preferably, in one embodiment where an HEV isemployed, the midpoint voltage selected for battery pack 14 avoids thepredetermined range of voltage described above, such as between about3.85 V and about 3.95 V. The midpoint voltage in HEV applications ischosen based on the battery packs ability to deliver both high dischargepower, as well as the ability to take high charging power duringregenerative breaking. The mid point is typically chosen to be at about50-60% state-of-charge. This state-of-charge setting then corresponds toa certain voltage, which depends on the chemistry in the battery. In aspecific embodiment, a voltage lower than about 3.85 V is selected forthe midpoint voltage of operation. In another specific embodiment, avoltage higher than about 3.95 V is selected for the midpoint voltage ofoperation.

The lithium-ion cells (or batteries) for the invention can be preparedby a suitable method known in the art. Typically, the lithium-ion cells(or batteries) include positive electrode, negative electrodes andelectrolytes in a cell casing. Such positive and negative electrodes,and electrolytes can be formed by suitable methods known in the art.

For example, a positive electrode can be produced by mixing the activepositive materials described above (e.g., Li_(1+x1)Mn₂O₄ and LiCoO₂) ata specific ratio. 90 wt % of this blend is then mixed together with 5 wt% of acetylene black as a conductive agent, and 5 wt % of PVDF as abinder. The mix is dispersed in N-methyl-2-pyrrolidone (NMP) as asolvent, in order to prepare slurry. This slurry is then applied to bothsurfaces of an aluminum current collector foil, having a typicalthickness of about 20 um, and dried at about 100-150° C. The driedelectrode is then calendared by a roll press, to obtain a compressedpositive electrode.

A negative electrode can be prepared, for example, by mixing 93 Wt % ofgraphite as a negative active material, 3 wt % acetylene black, and 4 wt% of PVDF as a binder. The negative mix was also dispersed inN-methyl-2-pyrrolidone as a solvent, in order to prepare the slurry. Thenegative mix slurry was uniformly applied on both surfaces of astrip-like copper negative current collector foil, having a typicalthickness of about 10 um. The dried electrode is then calendared by aroll press to obtain a dense negative electrode.

The negative and positive electrodes and a separator formed of apolyethylene film with micro pores, of thickness 25 um, are generallylaminated and spirally wound to produce a spiral type electrode element.

Examples of suitable negative active materials for the negativeelectrodes include any material allowing lithium to be doped or undopedin or from the material. Examples of such materials include carbonaceousmaterials, for example, non-graphitic carbon, artificial carbon,artificial graphite, natural graphite, pyrolytic carbons, cokes such aspitch coke, needle coke, petroleum coke, graphite, vitreous carbons, ora heat treated organic polymer compound obtained by carbonizing phenolresins, furan resins, or similar, carbon fibers, and activated carbon.Further, metallic lithium, lithium alloys, and an alloy or compoundthereof are usable as the negative active materials. In particular, themetal element or semiconductor element allowed to form an alloy orcompound with lithium may be a group IV metal element or semiconductorelement, such as but not limited to, silicon or tin. In particularamorphous tin, that is doped with a transition metal, such as cobalt oriron/nickel, is a metal that has high promise for anode material inthese type batteries. Oxides allowing lithium to be doped or undoped inor out from the oxide at a relatively basic potential, such as ironoxide, ruthenium oxide, molybdenum oxide, tungsten oxide, titaniumoxide, and tin oxide, and nitrides can be similarly usable as thenegative active materials.

Examples of suitable non-aqueous electrolytes include a non-aqueouselectrolytic solution prepared by dissolving an electrolyte salt in anon-aqueous solvent, a solid electrolyte (inorganic electrolyte orpolymer electrolyte containing an electrolyte salt), and a solid orgel-like electrolyte prepared by mixing or dissolving an electrolyte ina polymer compound or the like.

The non-aqueous electrolytic solution is typically prepared bydissolving a salt in an organic solvent. The organic solvent can includeany suitable type that has been generally used for batteries of thistype. Examples of such organic solvents include propylene carbonate,ethylene carbonate, diethyl carbonate, dimethyl carbonate,1,2-dimethoxyethane, 1,2-diethoxyethane, γ-butyrolactone,tetrahydrofuran, 2-methyl tetrahydrofuran, 1,3-dioxolane,4-methyl-1,3-dioxolane, diethyl ether, sulfo lane, methylsulfolane,acetonitrile, propionitrile, anisole, acetate, butyrate, propionate andthe like. It is preferred to use cyclic carbonates such as propylenecarbonate, or chain carbonates such as dimethyl carbonate and diethylcarbonate. These organic solvents can be used singly or in a combinationof two types or more.

Additives or stabilizers may also be present in the electrolyte, such asVC (vinyl carbonate), VEC (vinyl ethylene carbonate), EA (ethyleneacetate), TPP (triphenylphosphate), phosphazenes, biphenyl (BP), lithiumbis(oxalato)borate (LiBoB), ethylene sulfate (ES) and propylene sulfate.These additives are used as anode and cathode stabilizers or flameretardants, which may make a battery have higher performance in terms offormation, cycle efficiency, safety and life.

The solid electrolyte can include an inorganic electrolyte, a polymerelectrolyte and the like insofar as the material has lithium-ionconductivity. The inorganic electrolyte can include, for example,lithium nitride, lithium iodide and the like. The polymer electrolyte iscomposed of an electrolyte salt and a polymer compound in which theelectrolyte salt is dissolved. Examples of the polymer compounds usedfor the polymer electrolyte include ether-based polymers such aspolyethylene oxide and cross-linked polyethylene oxide, polymethacrylateester-based polymers, acrylate-based polymers and the like. Thesepolymers may be used singly, or in the form of a mixture or a copolymerof two kinds or more.

A matrix of the gel electrolyte may be any polymer insofar as thepolymer is gelated by absorbing the above-described non-aqueouselectrolytic solution. Examples of the polymers used for the gelelectrolyte include fluorocarbon polymers such as polyvinylidenefluoride (PVDF), polyvinylidene-co-hexafluoropropylene (PVDF-HFP) andthe like.

Examples of the polymers used for the gel electrolyte also includepolyacrylonitrile and a copolymer of polyacrylonitrile. Examples ofmonomers (vinyl based monomers) used for copolymerization include vinylacetate, methyl methacrylate, butyl methacylate, methyl acrylate, butylacrylate, itaconic acid, hydrogenated methyl acrylate, hydrogenatedethyl acrylate, acrylamide, vinyl chloride, vinylidene fluoride, andvinylidene chloride. Examples of the polymers used for the gelelectrolyte further include acrylonitrile-butadiene copolymer rubber,acrylonitrile-butadiene-styrene copolymer resin,acrylonitrile-chlorinated polyethylene-propylenediene-styrene copolymerresin, acrylonitrile-vinyl chloride copolymer resin,acrylonitrile-methacylate resin, and acrlylonitrile-acrylate copolymerresin.

Examples of the polymers used for the gel electrolyte include etherbased polymers such as polyethylene oxide, copolymer of polyethyleneoxide, and cross-linked polyethylene oxide. Examples of monomers usedfor copolymerization include polypropylene oxide, methyl methacrylate,butyl methacylate, methyl acrylate, butyl acrylate.

In particular, from the viewpoint of oxidation-reduction stability, afluorocarbon polymer can be preferably used for the matrix of the gelelectrolyte.

The electrolyte salt used in the electrolyte may be any electrolyte saltsuitable for batteries of this type. Examples of the electrolyte saltsinclude LiClO₄, LiAsF₆, LiPF₆, LiBF₄, LiB(C₆H₅)₄, LiB(C₂O₄)₂, CH₃SO₃L₁,CF₃SO₃Li, LiCl, LiBr and the like. Generally, a separator separates thepositive electrode from the negative electrode of the batteries. Theseparator can include any film-like material having been generally usedfor forming separators of non-aqueous electrolyte secondary batteries ofthis type, for example, a microporous polymer film made frompolypropylene, polyethylene, or a layered combination of the two. Inaddition, if a solid electrolyte or gel electrolyte is used as theelectrolyte of the battery, the separator does not necessarily need tobe provided. A microporous separator made of glass fiber or cellulosematerial can in certain cases also be used. Separator thickness istypically between 9 and 25 μm.

The electrolyte is then vacuum filled in the cell casing of alithium-ion battery where the cell casing has the spirally wound “jellyroll”. One or more positive lead strips, made of, e.g., aluminum, areattached to the positive current electrode, and then electricallyconnected to the positive terminal of the batteries. A negative lead,made of, e.g., nickel metal, connects the negative electrode, and thenattached to the negative terminal, for example, via a feed-throughdevice known in the art.

EXEMPLIFICATION Example Stability and Capacity of Li-Ion Cells Stored atVarious Voltages

In this example, it is shown that for Li-ion batteries, in particularfor Li-ion batteries containing a mixture of a lithium cobaltate and amanganate spinel, the voltage level of a given cell is a determiningfactor for the calendar life of the cell. This example shows that thereis a particular voltage range where Li-ion cells degrade faster. It istherefore desired, in order to enhance calendar life in batteries to asmuch as possible avoid this voltage range during use or storage of abattery having these characteristics. In particular, it has been foundthat for batteries containing a mixture having spinel in the cathode anda graphite anode, a storage voltage range between approximately 3.85Vand 3.95V is detrimental to calendar life. In addition, the voltagerange between 4.15V and 4.20V is also found to have increaseddegradation. This is believed to be due to very low rate chemicalreactions that dissolve metal ions from the cathode structure, inparticular for cathodes that contain manganese oxides of spinelstructure. Upon this dissolution the structural integrity of theelectrode is gradually destroyed and capacity is degraded.

Test Procedures

Cells were prepared by methods known in the art, for example, by methodsdisclosed in PCT/US2005/047383 and a U.S. patent application entitled“Lithium-ion Secondary Battery,” filed on June 23 under the applicationSer. No. 11/474,056, the entire teachings all of which are incorporatedherein by reference. A mixture of LiCoO₂ (70 wt %) and Li_(1+x1)MnO₄ (30wt %) was used as an active cathode materials for these cells. The cellswere stored for two weeks at 60° C. at various voltages, representing aselection of states-of-charge in the cell. 60° C. was selected as thehigher temperature would expedite faster degradation than roomtemperature measurements. The cells were then fully discharged to testfor remaining capacity in the cell. In order to check for recoverablecapacity, the cells were then recharged to full state-of-charge (4.2V)and discharged again to test for recoverable capacity of the cells.

In addition to capacity of the cells, the relative change of thicknessincrease also was measured in the cells, as this is believed to be ameasure of amount gassing due to irrecoverable loss of lithium from thecathode electrode and would relate to voltage stability.

TABLE 1 Thickness increase, retained and recovered capacity for cellsstored at 60° C. for two weeks Storage voltage (V) 4.2 4.1 4.0 3.9 3.8Retained Capacity 86.37% 88.48% 88.11% 79.08% 76.33% Recovered Capacity94.89% 95.03% 94.80% 90.92% 94.60% Thickness increase 0.64% 0.51% 0.51%1.08% 0.75%

Table 1 summarizes the observed values for these measurements. As shownin Table 1 above, the retained capacity was found to be at maximumbetween approximately 3.95V and 4.15V. At voltage higher than 4.1V, theretained capacity was lowered and at voltages lower than 3.9V, thecapacity was significantly lowered.

The relative thickness increase of the cells followed the trend of therecoverable capacity with the higher thickness increase at voltagesabove 4.1V and voltages below 3.9V. This may be at least partly due toboth gassing type reactions as well as regular expansion/contraction ofthe electrode due to the change crystal lattice parameter of the activematerials as lithium is moving in and out of the crystal structures.This expansion/contraction action causes permanent increase of electrodethickness resulting in a net expansion of the cell thickness. It istherefore reasonable to assume that limited increased gassing isoccurring between two ranges, of about 4.15-4.2V and about 3.85-3.95V.It is likely so that chemical and physical features at the interfacebetween the electrode materials and the electrolyte allows for enhancedreactivity, and therefore also for lowering of retained and recoverablecapacity in the voltage ranges specified. The lowering of retainedcapacity comes from permanent loss of lithium to reaction products onthe interfaces and gas, while the recoverable capacity loss is fromself-discharging mechanism, which is not producing a net loss of lithiumin the active materials. Another result of this increased reactivity atthe interfaces for certain voltage ranges is enhanced gassing, whichgradually builds up pressure inside the cells. The recovered capacitywas lower for the measurement at 3.9V, leading to a conclusion that thevoltage range of about 3.85V to about 3.95V is particularly bad for thecalendar life.

EQUIVALENTS

While this invention has been particularly shown and described withreferences to preferred embodiments thereof, it will be understood bythose skilled in the art that various changes in form and details may bemade therein without departing from the scope of the inventionencompassed by the appended claims.

1. A method of controlling a storage voltage of a battery pack withcontrol electronics for an electronic device, comprising the steps of:a) sensing a storage voltage of one or more cells of the battery pack;b) sensing a change in the storage voltage over a time period; c)determining, for the time period: i) whether the storage voltage iswithin a predetermined range of voltage at any time during that timeperiod, ii) whether the storage voltage is at or above a predeterminedvoltage at any time during that time period, and iii) whether the changein the storage voltage over the time period is at or below a thresholdrate of change; and d) triggering a discharge mechanism if, i) thechange in the storage voltage over the time period is at or below thethreshold rate of change, and the storage voltage is within thepredetermined range of voltage at any time during that time period, tothereby adjust the storage voltage to below the predetermined range ofvoltage; or ii) the change in the storage voltage over the time periodis at or below the threshold rate of change, and the storage voltage isat or above the predetermined voltage at any time during that timeperiod, to thereby adjust the storage voltage to below the predeterminedvoltage.
 2. The method of claim 1, wherein the threshold rate of changeis about 0.05 V/day.
 3. The method of claim 2, wherein the thresholdrate of change is about 0.03 V/day.
 4. The method of claim 1, whereinthe predetermined storage voltage is a voltage of a fullstate-of-charge.
 5. The method of claim 1, further comprising detectingwhether the battery is in a charging mode.
 6. The method of claim 5,further comprising: determining whether the time in the charging mode isgreater than a threshold time period; and discharging the battery to asecond predetermined voltage if the time in the charging mode is greaterthan a threshold time period.
 7. The method of claim 1, wherein thebattery pack includes at least one lithium-ion cell.
 8. The method ofclaim 7, wherein the predetermined range of voltage is selected from thegroup consisting of between about 3.85 V and about 3.95 V, and betweenabout 4.15 V and about 4.20 V, and wherein the predetermined voltage isabout 4.20 V.
 9. A system, comprising: a) an electronic device; b) abattery pack; and c) control electronics coupled to the electronicdevice and the battery pack, the control electronics: i) sensing astorage voltage of one or more cells of the battery pack; ii) sensing achange in the storage voltage over a time period; iii) determining, forthe time period: 1) whether the storage voltage is within apredetermined range of voltage at any time during that time period, 2)whether the storage voltage is at or above a predetermined voltage atany time during that time period, and 3) whether the change in thestorage voltage over the time period is at or below a threshold rate ofchange; and iv) triggering a discharge mechanism if, 1) the change inthe storage voltage over the time period is at or below the thresholdrate of change, and the storage voltage is within the predeterminedrange of voltage at any time during that time period, to thereby adjustthe storage voltage to below the predetermined range of voltage; or 2)the change in the storage voltage over the time period is at or belowthe threshold rate of change, and the storage voltage is at or above thepredetermined voltage at any time during that time period, to therebyadjust the storage voltage to below the predetermined voltage.
 10. Thesystem of claim 9, wherein the control electronics includes a) adetector circuit to sense a voltage of the battery pack and time; and b)a controller circuit to control a voltage and a current of the batterypack.
 11. The system of claim 10, wherein the control electronics areimplemented into the battery pack.
 12. The system of claim 10, whereinthe control electronics are implemented into the electronic device. 13.The system of claim 10, wherein one of the detector circuit and thecontroller circuit is implemented into the battery pack, and one of thedetector circuit and the controller circuit is implemented into theelectronic device.
 14. The system of claim 9, wherein the battery packincludes a resistive load through which the storage voltage of thebattery pack is discharged.
 15. The system of claim 9, wherein thethreshold rate of change is about 0.05 V/day.
 16. The system of claim 9,wherein the predetermined storage voltage is a voltage of a fullstate-of-charge.
 17. The system of claim 16, wherein the threshold rateof change is about 0.05 V/day.
 18. The system of claim 9, furtherincluding a charging circuit to charge the battery pack from an externalpower source, wherein the charging circuit is coupled to the controlelectronics.
 19. The system of claim 18, wherein the charging circuit isin the battery pack.
 20. The system of claim 9, wherein the battery packincludes at least one lithium-ion cell.
 21. The system of claim 20,wherein the predetermined range of voltage is selected from the groupconsisting of between about 3.85 V and about 3.95 V, and between about4.15 V and about 4.20 V, and wherein the predetermined voltage is about4.20 V.
 22. A battery pack comprising: a) a pack housing; b) at leastone cell in the pack housing; and c) control electronics in the packhousing, the control electronics: i) sensing a storage voltage of one ormore cells of the battery pack; ii) sensing a change in the storagevoltage over a time period; iii) determining, for the time period: 1)whether the storage voltage is within a predetermined range of voltageat any time during that time period, 2) whether the storage voltage isat or above a predetermined voltage at any time during that time period,and 3) whether the change in the storage voltage over the time period isat or below a threshold rate of change; and iv) triggering a dischargemechanism if, 1) the change in the storage voltage over the time periodis at or below the threshold rate of change, and the storage voltage iswithin the predetermined range of voltage at any time during that timeperiod, to thereby adjust the storage voltage to below the predeterminedrange of voltage; or 2) the change in the storage voltage over the timeperiod is at or below the threshold rate of change, and the storagevoltage is at or above the predetermined voltage at any time during thattime period, to thereby adjust the storage voltage to below thepredetermined voltage.
 23. The battery pack of claim 22, wherein thecontrol electronics includes a) a detector circuit to sense a voltage ofthe battery pack and time; and b) a controller circuit to control avoltage and a current of the battery pack.
 24. The battery pack of claim22, further including a charging circuit to charge the battery pack froman external power source, wherein the charging circuit is coupled to thecontrol electronics.
 25. The battery pack of claim 22, wherein thebattery pack includes at least one lithium-ion cell.
 26. The batterypack of claim 25, wherein the predetermined range of voltage is selectedfrom the group consisting of between about 3.85 V and about 3.95 V, andbetween about 4.15 V and about 4.20 V, and wherein the predeterminedvoltage is about 4.20 V.